Alloys with a nickel-chromium base



United States Patent ()fi 3,065,072 Patented Nov. 20, 1962 ice 3,065,072 ALLOYS WITH A NICKEL-CHROMIUM BASE John Henry Gittns, Studley, and Reginald Massey Cook,

Kings Heath, Birmingham, England, assignors to The International Nickel Company, Inc., New York, N.Y.,

a corporation of Delaware No Drawing. Filed Mar. 29, 1960, Ser. No. 18,238

Claims priority, application Great Britain Apr. 2, 1959 4 Claims. (Ci. 75-171) The present invention relates to nickel-chromium alloys and, more particularly, to nickel-chromium alloys having very good creep properties at very high temperatures.

It is well known that the creep-resisting properties of alloys having a nickel-chromium base depend on the presence and amount of other alloy constituents. In particular, the presence of both aluminum and titanium is necessary to provide a precipitable phase of the Ni (Ti-A1) type and other hardening elements are commonly included when the alloys must have good creep properties at very high temperatures. A very severe test consists in subjecting an alloy to a stress of 7 tons per square inch at a temperature of 960 C. An alloy which has a life to rupture of 200 hours or more under these conditions may be regarded as having outstanding properties. Alloys in.-

' tended to withstand stress at 960 C. have hitherto contained cobalt and it is known to include molybdenum in them also. Although many attempts were made to provide alloys having outstanding properties, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that there is a critical relationship between the cobalt and molybdenum contents in nickel-chromium alloys adapted to be employed at high stress at elevated temperatures.

It is an object of the present invention to provide nickelance with this relationship, it is to be noted that alloys within the present invention such as alloy No. 1 given hereinafter having a carbon content of 0.2%, a molybdenum content of 7% and a cobalt content of 7.7% exhibit a life to rupture of about 344 hours when stressed at 7 long tons per square inch at 960 C. Again, at a carbon content of 0.3% a life to rupture of 400 hours under the same conditions was observed when the molybdenum content was about 6% and the cobalt content was about 10%. The aforementioned alloys also contained about 15% chromium, about 4.5% aluminum, about 2% titanium, about 0.005% boron and about 0.05% zirconium, with the balance essentially nickel.

The cobalt content is such that when it is subtracted from the sum of 2.2 times the molybdenum content and times the carbon content the resultant figure is from 16.9 to 18.4. In other words, the expression must be satisfied. The extreme limits for cobalt are therefore 6.3% and 15.7%.

The remaining composition of the alloys according to the invention is as follows: chromium from 14.6% to 15.4%, titanium from 1.9% to 2.3%, aluminum from 4.1% to 4.7%, zirconium from 0.04% to 0.08%, boron from 0.004% to 0.008% and silicon from 0.2% to 0.4%, the balance of the alloys except for impurities, being nickel.

The compositions of alloys (1 and 2) in accordance with the invention together with the compositions of five alloys (A through E) outside the invention and made by vacuum melting are set forth in the following table. The factor obtained by solving the equation is set forth for each under the heading Factor.

Alloy Percent Percent 00 Percent Mo Percent Ti Percent Percent Si Percent Zr Percent B Percent Ni Percent Al cobalt-chromium-molybdenum alloys having excellent resistance to creep at elevated temperatures.

Another object of the invention is to provide nickelcobalt-chromium-molybdenum alloys having a life to rupture of at least about 200 hours and up to at least about 400 hours when subjected to a load of 7 long tons per square inch at 960 C.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates nickel-chromium alloys wherein cobalt produces a solution-hardening effect, molybdenum a precipitation-hardening elfect and these two effects interact to produce the best resistance to creep. Within certain critical ranges of cobalt and molybdenum, the life to rupture under stress of 7 long tons per square inch (t.s.i.) at 960 C. is strikingly increased.

The carbon content is a material factor and the percentage contents of both cobalt and molybdenum depend on it.

According to the invention, the carbon content is from 0.2% to 0.3% and the molybdenum content plus 10 times the carbon content is at least 8.7%, but the molybdenum content does not exceed 8%. In other words, the expression 8 Mo (8.710 C) must be satisfied. Thus, the minimum molybdenum content is 5.7%. In accord- The alloys are preferably made by melting under vacuum. Vacuum melted, wrought alloys according to the invention are found to have a life to rupture of 200 hours and more when subjected to a stress of 7 long tons per square inch at 960 C. after a heat treatment consisting in heating for 1 /2 hours at 1200" C., air-cooling to room temperature, heating for 16 hours at 1050" C. and again air-cooling to room temperature. For example, the alloys as set forth in the foregoing table exhibited lives to rupture as set forth in the following table when subjected to a stress of 7 t.s.i. at 960 C.

Life to rupture (hours) 344 Although the present invention has been. described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be Alloy:

mUO lZ 8% molybdenum in an amount such that the molybdenum content plus 10 times the carbon content is at least 8.7% and containing cobalt in an amount such that the cobalt content subtracted from the sum of 2.2 times the molybdenum contentplus 50 times the carbon content results in a value of 16.9 to 18.4, and the balance being essentially nickel, said alloy being characterized by a life to rupture of at least 200 hours at 960 C. and 7 long tons per square inch.

2. An alloy characterized by high rupture life at temperatures on the order of 960 C. consisting essentially of, by weight, about 14.6% to about 15.4% chromium, about 1.9% to 2.3% titanium, about 4.1% to 4.7% aluminum, about 0.04% to 0.08% zirconium, about 0.004% to 0.008% boron, about 0.2% to 0.3% carbon, about 5.7% to 8% molybdenum, about 6.3% to 15.7% cobalt, about 0.2% to 0.4% silicon, and the balance being essentially nickel.

:3. An alloy characterized by high rupture life at temperatures on the order of about 960 0., consisting essentially of, by Weight, about 0.3% carbon, about 6% molybdenum, about 10% cobalt, about 15% chromium, about 4.5% aluminum, about 2% titanium, about 0.005% boron, about 0.05% zirconium and the balance essentially nickel.

4. An alloy characterized by high rupture life at temperatures on the order of 960 C. consisting essentially of, by weight, about 15.1% to 15.2% chromium, about 2.1% titanium, about 4.5% aluminum, about 0.04% zirconium, about 0.006% to 0.007% boron, about 0.2% to 0.3% carbon, about 0.3% silicon, about 6% to about 7% molybdenum, about 7.7% to 10% cobalt and the balance'essentially nickel.

References Cited in the file of this patent UNITED STATES PATENTS 2,920,956 Nisbet et al. Jan. 12, 1960 FOREIGN PATENTS 548,777 Canada Nov. 12, 1957 548,778 Canada Nov. 12, 1957 92,627 Norway Oct. 13, 1958 814,029 Great Britain May 27, 1959 UNITED STATES PATENT OFFICE CERTIFICATEv OF CORRECTION Patent No. 3,065,072 November 20, 1962 John Henry Gittus et alo It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 34, for "292 M0 5O C=C0" read 22 M0+5O C-Co Signed and sealed this 25th day of June 1963,

S EAL Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

1. A NICKEL-BASE ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT, ABOUT 14.6% TO 15.4% CHROMIUM, ABOUT 1.9% TO 2.3% TITANIUM, ABOUT 4.1% TO 4.7% ALUMINUM, ABOUT 0.04% TO 0.08% ZIRCONIUM, ABOUT 0.004% TO 0.008% BORON, ABOUT 0.2% TO 0.3% CARBON AND ABOUT 0.2% TO 0.4% SILICON, SAID ALLOY ALSO CONTAINING ABOUT 5.7% TO 8% MOLYBDENUM IN AN AMOUNT SUCH THAT THE MOLYBDENUM CONTENT PLUS 10 TIMES THE CARBON CONTENT IS AT LEAST 8.7% AND CONTAINING COBALT IN AN AMOUNT SUCH THAT THE COBALT CONTENT SUBSTRACTED FROM THE SUM OF 2.2 TIMES THE MOLYBDENUM CONTENT PLUS 50 TIMES THE CARBON CONTENT RESULTS IN A VALUE OF 16.9 TO 18.4, AND THE BALANCE BEING ESSENTIALLY NICKEL, SAID ALLOY BEING CHARACTERIZED BY A LIFE TO RUPTURE OF AT LEAST 200 HOURS AT 960*C. AND 7 LONG TONS PER SQUARE INCH. 